1. Field of the Invention
The present disclosure relates to an object detection method, an object detection apparatus as well as an image pickup apparatus including the object detection apparatus.
2. Description of the Related Art
Analysis of visual objects in images is important in processes of object recognition, image retrieval, image registration and the like. Such processes are involved in many application fields such as surveillance (for security), video forensics, medical image analysis for computer-aided diagnosis and the like. In particular, object recognition has attracted increasing attention due to the increasing demand for developing real-world-related systems.
In conventional object recognition methods, learning/training-based classifiers are used, for which a learning/training process of classifier parameters is indispensable. However, classifiers obtained by learning/training process using specific samples of one object (for example, a dog) may not obtain good performance on another object (for example, a cat). In order to make the classifiers obtain good performance on the other object, another learning/training process has to be newly performed using specific samples of the other object, in order to modify the classifiers from those for the one object to those for the other object. This is not flexible and takes a long time.
One method for solving the above problem is to train a general classifier for a specific type of objects (such as pets including both dogs and cats), but such a general classifier will make the precision down and detect objects about which the user is not concerned. For example, even if the user only wishes to detect a dog in an image, a cat will also be detected from the image.
Another method for solving the above problem is discussed in US patent application publication No. US2010014721A1, and US patent publication Nos. US7558408B1, US7555148B1, and US7551755B1. The method disclosed in these patent documents is to first use a general classifier for a type of objects (for example, a classifier for pets) to locate the position of a candidate object in the image, and then to use a specific classifier (for example, a classifier for a cat) to judge whether the candidate object is the exact object of interest. This method has been used in cameras. According to this method, several specific classifiers (for example, a classifier for a cat, a classifier for one dog and a classifier for another dog) can be registered in advance by the user, and the user can select one of the specific classifiers for the object to be focused on before shooting a picture. The camera can be configured to automatically focus on the object detected from the image displayed in the viewfinder.
However, the inventor found that the method disclosed in the above patent documents is also not good enough because specific objects that can be detected are still limited, and only specific objects which are registered in advance by the user can be detected.